1. Field of the Invention
The present invention relates to a thin-film magnetic head wafer on which ID information is recorded and a method for manufacturing such a wafer. The present invention also relates to a magnetic head obtained by providing various types of transducers on the thin-film magnetic head wafer and further relates to a record medium drive including such a magnetic head.
2. Description of the Related Art
Recently, a thin-film magnetic head having any of various structures often includes a magnetic head slider for use in a hard disk drive (HDD), a tape storage and a flexible (or floppy) disk drive (FDD), for example. Examples of wafers for such a thin-film magnetic head include sintered wafers having compositions such as Al2O3—TiC, SiC and ZrO2.
FIG. 1A illustrates a typical thin-film magnetic head slider 10. On its tracking side, this magnetic head slider 10 includes two side rails 11 that are arranged to be opposed to the surface of a magnetic disk. The surface of the thin-film magnetic head slider 10 on which the side rails 11 are provided is sometimes called an “air bearing surface (ABS)”. If the magnetic disk is rotated at a high velocity by a motor, for example, while the surface of the magnetic disk is pressed lightly by the side rails 11 of the magnetic head slider 10 by way of a head suspension, then an air layer will be formed on the surface of the magnetic disk and will reach the back surface of the air bearing surface of the slider 10. As a result, the magnetic head slider 10 is slightly lifted up. In this manner, the magnetic head slider 10 can perform read and write operations on the magnetic disk while “flying” near the surface of the disk so to speak.
A thin film 12, which causes a magnetic interaction with a recording medium such as a magnetic disk, is deposited on one end surface of the magnetic head slider 10. The thin film 12 is used to form part of an electrical/magnetic transducer. To indicate the type of the product, an identifier (ID or ID mark) 13 such as a serial number is inscribed on the other end surface of the magnetic head slider 10. Methods of inscribing an identifier 13 on sintered wafers are disclosed in Japanese Laid-Open Publications Nos. 9-81922, 10-134317 and 11-126311, for example.
While the magnetic head slider 10 is flying with the rotation of a recording medium such as a magnetic disk, the magnetic head slider 10 leans such that the end surface thereof with the thin film 12 deposited thereon is closest to the recording medium and such that the other end surface thereof with the identifier 13 recorded thereon is farthest from the recording medium. The gas flows along the air bearing surface (ABS) from the end surface with the identifier 13 recorded thereon (i.e., leading edge) to the end surface with the thin film 12 deposited thereon (i.e., trailing edge).
In a typical manufacturing process, the magnetic head slider 10 is obtained by cutting out a bar 20 shown in FIG. 1B from a sintered wafer 1 shown in FIG. 1C and then dicing the bar 20 into a great number of chips. The sintered wafer 1 includes a first principal surface (on the leading edge) and a second principal surface (on the trailing edge), which are parallel to each other. The first principal surface will be referred to herein as the “front surface” of the wafer while the second principal surface will be referred to herein as the “back surface” of the wafer for convenience sake.
In FIG. 1C, the end surface 4 of the sintered wafer 1 is parallel to the air bearing surface of the magnetic head slider 10 shown in FIG. 1A.
Recently, as the sizes of such a thin-film magnetic head have been decreased to reduce the sizes and weight of an electronic appliance, the thickness of the sintered wafer 1 (corresponding to the length L of the magnetic head slider 10) and the thickness T of each bar 20 (corresponding to the height of the magnetic head slider 10) have also been reduced. For example, a magnetic head slider, which is called a “pico-slider”, has a length L of about 1.2 mm and a thickness T of about 0.3 mm. For magnetic head sliders of such drastically reduced sizes, the sizes of characters to be inscribed on the slider should also be reduced correspondingly.
In the prior art, a laser marking method is often used to inscribe the identifier 13. In the laser marking method, the identifiers 13 shown in FIGS. 1A and 1B are written on the back surface 3 of the wafer 1 that is yet to be divided into the bars 20. After the ID marking process step is finished, various thin films 12 (such as insulating films and magnetic films) are stacked on the front surface 2 of the wafer 1.
Hereinafter, the conventional laser marking method will be described briefly with reference to FIG. 2.
In the laser marking method, the back surface 3 of the sintered wafer 1 is locally irradiated with a laser beam 6 that has been converged by a lens 5, thereby rapidly heating and vaporizing the irradiated portion of the wafer 1. In this case, a tiny concave portion is formed on the back surface 3 of the wafer 1, while the material of the sintered wafer 1 is scattered around and just a portion of the scattered material is deposited on the wafer 1 again. By scanning the back surface 3 of the wafer 1 with the laser beam 6, the concave portions can be arranged so as to form an arbitrary pattern on the back surface 3 (which will be referred to herein as a “concave pattern”). Any of various types of identifiers 13 can be written at an arbitrary location on the wafer 1 by forming a concave pattern, which is made up of alphanumeric and/or numeric characters or a barcode, on the back surface 3 of the wafer 1.
FIG. 3 schematically illustrates a cross section of a sintered wafer 1 that has been marked by the conventional laser marking method. This cross-sectional view is drawn after a scanning electron microscope (SEM) photograph has actually been taken. As shown in FIG. 3, a deep concave portion 30 is formed on the surface of the wafer 1 as a result of the laser beam exposure. As measured from the back surface of the wafer 1 in the direction indicated by the arrow a in FIG. 3, the concave portion 30 has a depth of about 30 μm to about 50 μm. A convex portion (or burr) 31 is also formed around the edge of the concave portion. As also measured from the back surface of the wafer 1 in the direction indicated by the arrow b, the burr 31 has a height of several μm. The concave portion may have a width of about 20 μm, for example.
In the conventional laser marking process, however, the portion of the sintered material that has been scattered around as a result of the exposure to the laser beam is likely adsorbed or deposited as dust onto the inscribed characters, thus causing a contamination problem in many cases.
As shown in FIG. 3, a huge number of particles 32 are deposited on the inner surface of the deep concave portion 30 that has been formed as a result of the laser beam exposure. Strictly speaking, some of those “particles” 32 may have irregular shapes that cannot be classified among “particles”. However, those with irregular shapes will also be referred to herein as “particles” for the sake of simplicity. To remove those particles 32 from the wafer 1, a cleaning process such as an ultrasonic cleaning process must be carried out for a long time after the marking process is finished. Even so, it has still been difficult to remove most of the particles 32 that have reached the depth of the concave portion 30.
If a huge number of particles 32 are created during the marking process, some of those particles may be dispersed in the cleaning liquid and then deposited on the other side (i.e., the front surface 2) of the wafer 1 that has not been exposed to the laser beam. In that case, when an insulating thin film of alumina, for example, is deposited on the front surface 2 of the wafer 1 with the re-deposited particles 32, then those particles 32 might be introduced into the insulating film. Also, the surface of such an insulating thin film is normally planarized before a magnetic thin film is deposited thereon. Accordingly, if the insulating thin film includes the particles 32, portions of the insulating thin film may peel off locally along with the particles 32 to possibly create pinholes in the insulating thin film during the planarizing process. Also, even if no such pinholes have been created, a portion of the insulating thin film may have its thickness decreased significantly by the particles 32. Then, that portion of the insulating thin film may exhibit decreased insulating properties. Furthermore, even when no such particles enter the insulating film, the marks on the back surface of the wafer 1 may still be a dust source. Then, the yield may decrease in a number of subsequent manufacturing process steps, and the quality of the final product itself may deteriorate.
Also, as the storage capacity of HDDs has been further increased recently, the distance between the magnetic head and the recording medium (i.e., magnetic disk) during a read or write operation has been further decreased. Thus, the presence of even a very small amount of particles may cause a serious error in the operation of an HDD. Accordingly, if the concave portion formed on the back surface of a wafer to record ID information thereon traps dust, then the concave portion may be a dust source during the read or write operation. In that case, the reliability of a recording medium drive such as an HDD may deteriorate significantly.